1. Field of the Invention
The present invention relates generally to preforms for use in construction of vehicles and relates specifically to preforms used for forming acute structural edges.
2. Description of the Related Art
When constructing vehicles, it is often desirable or necessary to create edges formed using acute angles. This is especially true when constructing air vehicles, such as manned or unmanned aircraft and missiles, which may require a sharpened edge for smoothly penetrating the airflow or providing a smooth convergence of separate flows.
FIG. 1 shows a prior art aircraft 11 and illustrates the numerous locations of acute structural edges. The most common use of acute edges is in leading edges 13, 15 and trailing edges 17, 19 of wings 21, 23, respectively. Leading edges 13, 15 ensure that wings 21, 23 pass easily through a longitudinal airflow, whereas trailing edges 17, 19 allow the separated airflows on either side of wings 21, 23 to smoothly converge at the rear of wings 21, 23. Inlet lips 25 separate onrushing air into flows entering engine nacelles 27 and flows continuing on the outer surfaces of aircraft 11. Chines 29 are formed along longitudinal edges, providing desired aerodynamic effects and a blended shape for reducing radar cross-section.
FIGS. 2 through 4 illustrate prior art methods for forming acute structural edges. Though described in terms of directions relative to their orientation in the figures in the present application, it should be noted that the edges may be located in various orientations, including orientations opposite of those shown or in inclined or vertical orientations.
In FIG. 2, assembly 31 is formed by inserting a rigid edge member 33 between an upper planar element 35 and a lower planar element 37. Edge member 33 and elements 35, 37 may be formed from various materials, including metals and composites. When assembled, upper surface 39 of edge member 33 registers with the outer surface of element 35 and lower surface 41 registers with lower element 37, forming smooth, continuous outer surfaces for undisturbed airflow. A forward edge 43 has an acute included angle and is located on the forward portion of edge member 33. Members 45 extend from a rearward portion of edge member 33 for fastening edge member 33 to elements 35, 37. Members 45 are inwardly offset toward a plane (not shown) bisecting edge member 33 and parallel to forward edge 43, forming rearward-facing shoulders 47. The forward ends of elements 35, 37 abut shoulders 47. Typical methods of fastening edge member 33 to elements 35, 37 include adhering members 45 to the inner surfaces of elements 35, 37 and mechanically fastening members 45 to elements 35, 37.
FIG. 3 shows assembly 49, which is formed by assembling upper element 51 with lower element 53, elements 51, 53 being formed of rigid materials, such as metals or composites. Elements 51, 53 terminate in forward ends 55, 57, respectively, each forward end 55, 57 having an increased thickness and mating surface. When elements 51, 53 are assembled to each other, the mating surfaces are adjacent at seam 59 and forward ends 55, 57 are aligned to form forward edge 61. Elements 51, 53 are fastened together at forward ends 55, 57 by fastener 63, for example, a double-countersunk fastener, which extends through the thickness of the assembled forward ends 55, 57.
Like assembly 49 in FIG. 3, edge assembly 65 in FIG. 4 comprises upper element 67 and lower element 69. Upper element 67 has a forward end 71 having an increased thickness and a downward-facing mating surface. Lower element 69 has a forward end 73 that also has an increased thickness and an upward-facing mating surface. Elements 67, 69 are aligned and joined to each other, the mating surfaces being adjacent at seam 75 and forward ends 71, 73 aligning to form forward edge 77. Rather than being joined using fasteners, elements 67, 69 adhered to each other or bonded in a co-curing process.
While these prior art assemblies have satisfactorily been used to form acute edge structures, improvements are needed to reduce weight and cost and increase structural integrity of edge structures. Additionally, improvements are needed to improve the ability to repair damaged edge structures and to allow for tailored material and structural properties.
An apparatus and method are provided for constructing acute structural edges. A preform has a body having an acute-angle edge at one end and connecting areas extending from the opposing end for bonding the preform to converging planar elements of a wing or other similar structure. In several embodiments, the acute angle of the preform generally matches the angle relative to each other of converging ends of the planar elements, the preform forming the outer end of smooth, continuous outer surfaces after assembly. The connecting areas may be connected to interior or exterior surfaces of the elements, depending on the orientation of the preform and elements. In another embodiment, the preform is placed between the outer ends of the elements for aligning and supporting the elements at the desired location and angle relative to each other.